1. Field of the Invention
The present invention relates to the preparation of decorated resin films, and particularly to the preparation of such films as are metalized on selective areas.
2. Description of the Prior Art
Selectively decorated films have had a variety of decorative and technical utilities that have made them popular over the years. In particular, selective metalization has been utilized for products as divergent as gift wrapping paper, embellished mirrors and electrical apparatus, the latter of increasing importance with the advent of the broad usage of printed circuit technology.
For example, U.S. Pat. No. 2,000,310 to White et al discloses the use of a resist coating which is applied to the rear surface of glass so that a particular design may be defined on the mirror after silvering of the glass surface is completed and the resist is removed. The technology in White et al relates to the old art of silvering and is distinguishable from the present invention.
In U.S. Pat. No. 2,139,640 to Mall et al, the patentees employed a grease or oil substance as a mask on surfaces to be metalized, to achieve selective metalization or pattern making. The use of oil or grease results in a liquid coating which remains in the liquid state after metalization, so that removal of the excess metal is accomplished by wiping the surface to remove the oil or grease mask. This technique would be unsuitable for use with the metalized products prepared for contemporary applications.
More recently, numerous approaches have been taken in an effort to adapt the technique of selective metalization by use of a resist or mask, to the production of printed circuit boards or integrated circuits (ICs). Thus, U.S. Pat. No. 3,554,780 to Miller et al discloses the use of an acid-resistant coating as a resist or mask, which may be a dispersion of vinyl copolymers having at least 4% by weight of a carboxylic acid. The mask is removable by an alkaline agent such as ammonium hydroxide. The drawback of the use of the Miller et al system is its limited applicability by virtue of the use of an alkaline solvent, and the possibility that such solvent may attack certain of the materials used in a particular metalized lamination or the like.
A more pertinent disclosure is that of U.S. Pat. No. 3,935,334 to Narui et al. In this patent, a water soluble coating is applied within specific critical thickness limits by techniques such as screen printing, gravure coating and the like, to give a specific coating pattern. Thereafter, the surface bearing the dielectric coating and the masking coating on top of it, are metalized. After metalization is complete, the surface may be washed with water, and the water soluble mask will dissolve, taking with it the portion of the metal layer deposited thereover. As noted, the Narui et al system requires the observance of specific tolerances in the thickness of the resist layer to be fully operable.
A variety of alternate techniques utilizing solvents and/or photopolymerizable compositions to which masks or resists are applied are disclosed in the following U.S. Pat. Nos. 4,059,708 to Heiss, Jr. et al; 4,089,686 to Townsend; 4,270,985 to Lipson et al; and, 4,346,125 to Kinsbron et al.
While the above techniques have all been directed to overcome the deficiencies noted in the prior art with regard to the masking methods for selective metalization, many of these deficiencies still remain. Thus, it is noted that Narui et al discusses a variety of techniques including the tape-masking method and oil-masking method and distinguishes these methods and their deficiencies by noting that the prior art methods failed to define an acceptable "margin edge". The "margin edge" is, as it implies, the border or perimeter of the metalized layer that is defined when the mask or resist is removed from the metal-coated film or base. The solvent-based techniques exemplified by Narui et al have been tested and suffer from the same deficiencies that the patentees outlined with respect to the prior art. Thus, and particularly in the instance where such techniques are employed to mass produce decorative selectively metalized film, the resulting products exhibits either a non-uniform marginal edge, or in some instances such as in the case of intricate metal designs, the entire design is distorted and frequently bears an etched appearance.
Added to the foregoing visual deficiencies in the final product, are the complexities and inefficiencies of the solvent based system. The product must therefore be exposed to solvent action which by itself is difficult to control, and to such extent, detracts from the uniformity and reproducibility of the desired selective pattern.
A need therefore exists for a method for the selective metalization of resinous materials which is highly reproducable and offers a superior marginal edge with a minimum of criticality and complexity in post-metalization processing.